Layered Europium and Yttrium Hydroxychlorides: Thermal Decomposition and Rehydration

The dehydration–rehydration process of layered hydroxides is an example of a reversible chemical reaction involving rearrangement of the crystal structure. Products of thermal decomposition of layered rare earth hydroxides are known to react under certain conditions with aqueous salt solutions and restore their original layered structure. In the present work, the effect of the temperature and duration of thermal treatment of the layered rare earth hydroxychlorides at 100–1150°C on the reaction of the obtained products with aqueous sodium chloride solution was systematically studied for the first time. The main stages of the thermal decomposition of layered rare earth hydroxychlorides were determined by the thermogravimetric analysis. X-ray powder diffraction analysis and energy-dispersive X-ray spectroscopy were used to determine the phase and the chemical composition of the products of thermal treatment and subsequent rehydration of the layered hydroxides. It was shown that the presence of the rare earth oxychloride phase in the products of thermal decomposition was a critical factor for the recovery of the layered structure.